This invention generally relates to agricultural mulches. Specifically, this invention relates to biodegradable agricultural mulches which may remain in the soil after their use.
Plastic mulches are widely used in numerous agricultural applications to control weeds, retain moisture in the soil and increase soil temperature to facilitate plant growth and to increase crop quality and yield.
Desirable characteristic for a mulch include having sufficient mechanical strength so that they may be used in commercial farming operations with heavy duty equipment, resistance to stresses caused by weather (rain, sun, wind, etc.), puncture resistance to growing weeds, sufficient wet strength, moisture retention and ultraviolet light absorption. It is also important that standard agricultural equipment be able to till the mulch into the soil at the end of the growing season so that the mulch need not be removed in a separate and expensive operation.
A wide variety of mulch products have been developed in an attempt to meet the above requirements. Traditionally, agricultural mulch films have been predominantly comprised of either low or high density polyethylene because they are relatively inexpensive and more resistant to severe weather conditions than other materials. However, these materials are not considered biodegradable and must be removed and land filled at the end of the growing season.
To address the biodegradability problem some conventional mulches are made from paper. However, paper generally degrades too quickly, does not retain sufficient ground moisture or lacks sufficient strength to be used in commercial agricultural operations. Coating paper with various compounds such as polyethylene, polypropylene, or polyvinyl chloride, polyvinyldene chloride, styrene butadiene, carboxylated styrene butadiene, carboxylated acrylonitrile butadiene, and natural rubber latex may increase its strength and slow its degradation rate. However, the coating must be completely biodegradable and incorporate all of the features discussed above for the paper/coating substrate to function as a useful agricultural mulch.
U.S. Pat. Nos. 3,810,328, 3,938,280 and 3,939,606 disclose paper-based mulches with coatings that include organic resin or plastic coatings such as polyethylene, polypropylene, polyvinyl chloride, wax-based coatings, polyvinyl acetate, Saran or similar coatings.
U.S. Pat. Nos. 4,782,626, 5,163,247, 5,672,434 and 5,866,269, disclose paper or cellulose fiber mulches with latex coatings or related methods.
U.S. Pat. Nos. 5,532,298 and 5,853,541 disclose agricultural mulches made by combining mixtures of linters, pulps and water holdout materials or pulps, polyethylene fibers and, optionally, water holdout materials.
U.S. Pat. No. 5,191,734 discloses a mulch comprised of biodegradable cellulose or synthetic fiber web treated with latex.
U.S. Pat. No. 5,096,941 discloses a degradable composition comprised of polyethylene and cerium stearate which can be made into a film and used as an agricultural mulch.
All of these references concern mulches which may contain non-biodegradable material.
U.S. Pat. No. 5,934,011 discloses a seed mat comprised of a water soluble paper layer, a water absorbing polymer film layer and seeds.
U.S. Pat. No. 6,033,747 discloses the use of various biodegradable polyesters comprised of poly (3-hydroxybuturate-co-3-hydroxyhexanoate) to laminate base materials to form agricultural mulches.
U.S. Pat. No. 6,040,063 discloses biodegradable hydroxy functionalized polyester compounds and mulches made therefrom.
U.S. Pat. Nos. 5,863,991, 5,880,220, 5,889,135, 5,936,045, 6,018,004, 6,046,248, 6,111,058, 6,114,042 and 6,103,858 disclose biodegradable polyester compounds with various applications.
U.S. Pat. Nos.5,292,783, 5,466,079, 5,580,911, 5,599,858 and 5,900,322 are related cases which disclose various chemical compounds, including polyesters, with various applications.
While a variety of products exist, none possess all of the qualities that are desirable for an agricultural mulch. Thus, there is a need for a truly biodegradable agricultural mulch which will not build up and remain in the soil after tilling and which incorporates the desirable features and characteristics described above.
The present invention is a paper-based agricultural substrate/mulch, which is biodegradable, has sufficient mechanical strength for commercial operations and retains a sufficient ground moisture. Other advantages include adjustable biodegradation rates and wet strength, resistance to natural stresses, such as weather, and the ability to be tilled or disked into the soil with standard agricultural equipment.
The preferred embodiments, when used in an agricultural application, will eventually degrade to water, CO2 and biomass. This complete biodegradation distinguishes the mulches of the invention from many existing mulches which may break down to small pieces when tilled but biodegrade slowly so that they remain in the soil for several planting seasons.
In accordance with one preferred embodiment of the invention a substrate comprising a paper layer and an extruded biodegradable polymer layer is provided.
In accordance with another preferred embodiment of the invention a substrate comprising a paper layer and a co-extrusion of two or more biodegradable polymer layers on the same side of the paper layer is provided.
In accordance with another preferred embodiment of the invention a substrate comprising a paper layer and at least one extruded biodegradable polymer layer on each side of the paper layer is provided.
In accordance with another preferred embodiment of the invention a substrate comprising a paper layer, at least one polymer layer and various additives in the polymer layer suited to the particular use of the substrate is provided.